The present application applies to radiation flux in Computed Tomography (CT) equipment. While it applies to a variety of computed tomography equipment, it finds particular application to security examination equipment, such as baggage systems commonly found in airports and government buildings.
Computed Tomography, in general, generates a three-dimensional image of an object from a series of two-dimensional images taken around a single axis of rotation. An object under examination is exposed to radiation, and images are formed based on the radiation absorbed by the object, or rather an amount of radiation that is able to pass through the object. Highly dense objects absorb more radiation than less dense objects, and thus an object having a high density, such as a metal gun, for example, will be apparent when surrounded by less dense objects, such as clothing.
In baggage systems, Computed Tomography equipment is used to detect weapons, explosives, and other prohibited items that may be contained in a suitcase or bag being scanned. One type of CT baggage scanner is described in U.S. Pat. No. 6,256,404 to Gordon et al. In particular, an x-ray tube and a detector array are mounted on diametrically opposing sides of an annular shaped rotating platform, or disk, disposed within a gantry support for rotation about a single axis that is parallel to the direction of travel of the baggage (e.g., along a conveyor system). The x-ray tube emits x-rays at a fixed radiation flux rate, and the x-rays traverse the baggage under examination. X-rays that are not absorbed by the baggage and/or objects therein are detected by a detector, and an image of the bag and the contents thereof may be created based on the detected x-rays.
While such a configuration has proven effective in detecting objects, there remains room for improvement. For example, the x-ray tube emits x-rays at a fixed rate, regardless of the object being scanned. If a dense bag, such as a laptop bag, is scanned, a large percentage of the emitted x-rays may be absorbed by the bag, causing a small percentage of the emitted x-rays to be detected by a detector, and an image of bag to be created wherein the contents are rendered indistinguishable. Additionally, x-rays are emitted during instances in which there are no objects being scanned, which may reduce the life of the x-ray tube unnecessarily.